A thermoplastic norbornene addition polymer that includes a polar functional group is transparent and has low dielectric constant and hygroscopic property. Furthermore, the norbornene addition polymer is excellent in terms of thermal stability, mechanical strength, and adhesion strength, and generates no byproducts when being attached to metal or other polymers. The norbornene addition polymer may be used in a polarizer protection film, an optical film such as a retardation film, a plastic substrate material, a transparent polymer such as POF, a PCB, or an insulating electronic material such as an insulating substance.
However, when an addition polymer is produced by using a norbornene monomer having a polar functional group, in the case where the monomer is the endo isomer, a polymerization speed is lower, a polymer has a lower molecular weight, and a polymerization yield is lower as compared to the case where the monomer is the exo isomer.
For example, according to Risse et al., if a norbornene derivative having a polar functional group such as an ester group is produced by using a palladium catalyst (Pd(CH3CN)4)[BF4]2), in the case where the ratio of endo isomer is higher among exo and endo isomers of the ester-norbornene monomer (exo/endo=20/80 and yield 23 to 30%), the polymerization yield and the molecular weight are lower as compared to the case where polymerization is performed by using only the exo isomer (yield 70% or more) ((a) Risse et al.; Makromol. Chem., 1992, Vol. 193, 2915-2927; (b) Risse et al.; Macromolecules, 1996, Vol. 29, 2755-2763).
The reason why the polymerization yield and the molecular weight are lower is that unshared electron pairs of the polar functional group of the endo type substituent are strongly bonded to vacant sites of a metal catalyst to prevent the norbornene monomers from approaching the metal, thereby slowing down the polymerization. For example, in the case where norbornene has an endo type ester group, a complex is stabilized and the unshared electron pairs of the oxygen atom partially provide electrons to the metal atom due to a chelate effect where an oxygen atom of a carbonyl group that is contained in the ester group is bonded to a metal catalyst. Thus, a catalytic activity of the metal atom is reduced ((a) Sen et al.; Organometallics 2004, 23, 1680-1683; (b) Sen et al.; Organometallics 2001, 20, 2802-2812; (c) Sen et al.; Ace. Chem. Res. 1993, 26, 303-310; (d) Risse et al. Macromolecules 1996, 29, 2755-2763.).
Accordingly, in the addition polymerization of the norbornene monomer having the polar functional group, only the exo isomer may be used or the monomer that contains the exo isomer in a large amount (an excessive amount of exo) may be used to significantly increase the molecular weight while the yield is not reduced during the production of the polymer. In addition, in the case where a film is produced by using the above-mentioned polymer, viscosity of a film production solution is increased, the modulus of the film is improved, and surface hardness is improved. Hence, it is possible to produce a film having excellent mechanical properties. Therefore, it is very important to ensure a reaction condition capable of controlling a ratio of norbornene isomers (endo and exo isomers).
However, a known method for producing a norbornene monomer having a polar functional group by using a catalyst such as a Lewis acid is problematic in that an endo isomer is generated in a large amount (Chem. Rev. 1961, 61, 537-562).
For example, in the case of a 5-norbornene-2-methyl acetate monomer, a production method by using norbornene methanol (bicyclo[2,2,1]hept-5-enyl-2-methanol) is known in the art. However, a plurality of stages are performed in the method, and the resulting compound contains the large amount of endo isomer so that a ratio of exo/endo isomers is 20/80 ((a) Castner, K. F.; Calderon, N. J. Mol. Catal. 1982, 15, 47.; (b) Risse et al.; Makromol. Chem. 1992, 193, 2915.; (c) Roberts et al.; J. Am. Chem. Soc. 1950, 72, 3116.; (d) Ver Nooy et al. J. Am. Chem. Soc. 1955, 77, 3586.; (e) Arjona et al. J. Org. Chem. 1991, 56, 6227.; (f) Nelson et al. Synthesis 1975, 105.; (g) Magoon et al. J. Organomet. Chem. 1973, 55, 409.).
That is, it is difficult to achieve synthesis of a pure exo isomer of 5-norbornene-2-methyl acetate by using a simple process, and a plurality of stages must be performed in known processes. Accordingly, there is a need to provide a method of industrially producing a norbornene monomer containing an excessive amount of exo isomer by using a simple process.
It is known that a sterical chemical of a product depends on polar or nonpolar properties of a solvent in a Diels-Alder reaction (Otto et al.; J. Am. Chem. Soc. 1996, 118, 7702). However, a ratio of an exo isomer product to an endo isomer product is not more than 33%.
Therefore, there remains a need to provide a method of industrially producing a norbornene monomer that is used to produce an addition polymer of the norbornene monomer having a polar functional group, has the polar functional group, and contains an excessive amount of exo isomer by using a simple process so that the yield of polymer is improved and the molecular weight is increased.